-This is a good question and not easily answered in the long run. Today's scanners basically take analog information and transform it into digital information made into a bitmap.
-Now, how does all this work and how does a scanner actually grab a snapshot of a photo? All scanners take the same basic approach to scanning . A light source or array lines up with your document horizontally. This is so the document can illuminated and light is reflected back and detected by what is called a CCD. A CCD (charge coupled devices) converts the reflected light into electrical impulses. These impulses vary depending on the amount of light reflected. So say a photo of you in a black shirt may not send back as much light to the CCD. Now a CCD is important to know about when buying a scanner. The more the better. Now how do you know how many CCD's a scanner has? There is one CCD for every pixel of resolution. So, a scanner with 1200 dpi has 1200 CCD's. When you buy a scanner you will see a dpi rating for it such as "For Sale, 1200dpi scanner". By the way this is pretty good resolution and is also referred to as Optical Resolution. Also the CCD's are arrayed across the scanners sensor head. After the CCD grabs the light reflection it will be turned over to a analog to digital converter only to end up in your computer's software.
Scanners - How They Work?
